FIG. 1 shows a circuit diagram adapted to be used to supply a load L from a mains supply N (for example a 220V/50 Hz or a 120V/60 Hz supply, respectively according to the European and the American standard), through a so-called “double switching”, i.e. via a first and a second switch 10 and 12 adapted to be arranged, for example, in different positions in the same room, at both ends of a corridor, or upstairs and downstairs, so that each switch 10 and 12 can be used to activate and deactivate load L, for example in order to turn a light source on and off.
The aforementioned result can be obtained by providing a first electrical contact 14, adapted to connect one of the poles of supply N (for example the neutral pole) to one end of load L, and by implementing both elements 10 and 12 as switches.
Specifically, the first switch 10 is connected so as to be able to send the other pole 16 (for example the phase pole) of supply N alternatively to one or the other of two “hot” contacts 18, 20. Such contacts are sometimes referred to as “switched lines”, and are commonly named “travelers”.
The second switch 12 is designed so as to connect load L alternatively to one or the other contact 18 and 20 through a contact 22, opposed to the terminal connected with contact 14.
The operation of the connection arrangement depicted in FIG. 1 (also described in documents such as US-A-2007/0171625 or US-A-2010/0288609) is based on the fact that:                switch 10 allows to activate or deactivate load L on the basis of whether its movable contact is brought towards or away from the one contact, 18 or 20, which is currently connected, via switch 12, to the contact 22 referred to load L, and        switch 12 allows to activate or deactivate load L on the basis of whether its movable contact is brought towards or away from the contact, 18 or 20, which is currently connected to line 16 via switch 10.        
The chain-dotted line in FIG. 1 shows the possibility for the enclosed elements to form a single element, adapted to be mounted on a wall socket, for example in the form of a so-called embedded module.
Both aforementioned documents show moreover the possibility to associate, to the previously described circuit arrangement, an additional lighting source such as a LED, adapted to perform at least one function between locating the switch assembly in the dark and showing the fact that the load is currently activated or deactivated.